Apparatus for the production of sounds from electric current and inversely



June 3, 1930. c, ows ET AL 1,760,896

APPARATUS FOR THE PRODUCTION OF SOUNDS FROM ELECTRIC CURRENT AND INVERSELY Filed July 50, 1927 2 Sheets-Sheet l June 3, 1930. CJ'CHILOWSKY El AL 1,760,896

APPARATUS FOR THE PRODUCTION OF SOUNDS FROM ELECTRIC CURRENT AND INVERSELY Filed July 30,1927 2 Sheets-Sheet 2 Patented June 3, 193G UNITED STATES PATENT OFFICE oons'rmm 'cnr'nowsxx, or'rruais, amen, AND some naeacnnrr, or BOSTON massaonusnrrs APPARATUS FOR THE PRODUCTION OF SOUNDS FROM ELECTRIC CURRENT AND 1 INVERSELY Application filed Italy 80, 1927, Serial'No; 209,586, and in France August 7, 1926.

The known loud-speaking apparatus, which are based upon the attraction of electrostatic fields, are defective from the fact that they will not allow the use of short distances between the condenser sheets, or will not produce waves of sufiicient amplitude by reason of the damping action of the thin layer of air between the said sheets.

The present invention relates to a method and apparatus whereby all such defects will be obviated.

Our apparatus is characterized by the provision of apocket, one or two walls of which are vibrating diaphragms impermeable to air, and of one or two rigid sheets permeable to air, disposed either within the pocket or without, the variable potential of a vibrational electric current which is to be converted into sound waves being applied between said diaphragms and said sheets maintained at a very short distance from one another. a

An essential feature of our apparatus lies in the ability of adjusting the distance between vibrating diaphragms and rigid sheets by producing a vacuum or an excess of pressurein the interior of the pocket.

According to our invention, in the first case, in which a stationarymiddle sheet permeable to air is employed, the condenser comprises a flat element or sheet consisting of a substance which is a conductor oris rendered conducting and is permeable to air for the major part, such for instance as a sheet of wire gauze or of metallized fabric, a sheet of metal or metallized substance, which is finely perforated, or the like. Upon either side of the sheet is placed a layer of insulating material such as a very light silk fabric, thm paper, or the like, and also a condenser plate which may consist of a very thin leaf of metal such as gold, aluminium or the like, or of thin membranes of rubber, acetate of cellulose, cellulose or other substance, which are metallized on the exterior. In the case of metallized insulating membranes, the interposition of insulating fabric is not necessary.

.The middle metallic sheet is so chosen that it will possess per unitsurface, a mass of inertia which is preferablygreat with reference to the inertia of a column of air the surface of whose base is equal to unity and whose thickness represents one-half a wave-length, in air, of the sound produces or received. On the contrary the two external condenser sheets on either side of the said middle sheet are made as light as ossible, so that their inertia will be negligible with reference to the inertia of the half wave-length in air referred to.

When the apparatus is employed as a loud-speaking device, we apply a difference of potential, constant and sufiiciently great, to the respective external sheets. In the inoperative position, the said middle element or sheet ismaintained at a zero potential or at a potential which is a mean between that of said external sheets, and it isconnected, when operating, with the source of the variable potential of the vibrational current'to be converted into sound. Under the action of this current, the said middle element will be 111mm or less strongly charged, and will attract the outer sheets to a greater or less degree. The direction of this attraction or repulsion is represented by the direction of the constant field between the outer sheets and the sign of the charge of the middle element. Since the mass or inertia of the middle element is considerable and is usually much greater than that of the external sheets, the amplitude of the oscillations of the middle element, under the action of the variable electric charges, will remain small, and in practice the middle element will remain stationary, whereas the amplitude of the very light external sheets will be considerable, so that the soundwill be produced in the air. The two external sheets will oscillate in synchronism together-with of air is not subjected to any appreciable variation of pressure.

In the case in which the apparatus is employed as a microphone, the sound waves which strike the surface will cause the said sheets to oscillate, and these latter will remain together by reason of the thin layer of air between them; the middle element or sheet will be relatively stationary, so that variations in the charge and potential will be produced upon the surface, and these variations will then be amplified by known means.

The operation of the loud-speaking device depends to a great degree upon the method of applying the external sheets against the middle wire gauze member, for upon this method of application will depend the freedom obtainable for the mechanical oscillations and also the values of the electrostatic field. To regulate this application, we may employ means for varying the pressure of the gas or the air contained between the two external sheets, by producing between them a slight vacuum which assures the proper application, or by producing a slight excess of pressure which may partially counterbalance the force of the electrostatic attraction, thus giving the external sheets the maximum freedom of vibration.

In a modified construction, the said middle element may consist of two parallelsheets of an insulating substance consisting for example of acetate of cellulose, or preferably of cellophane, said sheets being joined together at the periphery so as to form a flat recipient or pocket, whose inner surfaces are made conducting by coating them with metal. The said pocket is'placed between the two wire gauze members, so that each face will be applied against the corresponding wire gauze member. Should the surface of the apparatus be considerable, each wall of the said middle recipient may be connected with the corresponding wire gauze member at a certain number of points, or along various lines, for instance by cementing, or by introducing small elastic balls into the said pocket by which its two walls will be placed against the wire gauze members.

In thls manner the v1brat1ng surface 1s dlvlded into a certain number of sections I which will vibrate under the effect of the electrostatic field. The vibrating sheet or membrane may be properly applied upon the wire gauze members by cementing it at a great number of points; but in order to give the spacing strips between the wire gauze members and the corresponding membranes of the said middle pocket or recipient, and by producing a slight excess of pressure in the interior of the said pocket, its walls may be brought nearer the said wire gauze members.

We use a slight vacuum or excess of pressure to regulate the application of the said surfaces and obtain the best application compatible with the required freedom of oscillation, thereby assuring the most approved functioning.

The said loud speaking apparatus may have a large size, and its dimensions may be considerable with reference to the wave length emitted in the air, so as to obtain a sound which is sent out in a given direction, in the shape of a narrow cone. In this manner we may obtain a loud-speaking device which acts after the manner of a speaking trumpet.

Our invention will be more readily understood by reference to the following description when taken in connection with the accompanying drawing forming part of this specification and in which Fig. 1 is a diagrammatic view showing in section a constructional form of our said apparatus. In this diagrammatic figure and the following, the distances between the membranes or diaphragms are exaggerated for the sake of clearness.

Fig. 2 is a detail view on a larger scale.

Fig. 3 shows a modified apparatus, and Fig. 4 another modification.

Fig 5 showsthe utilization of our said apparatus as a listening device.

Figs. 6 and 7 show two other modifications.

Fig. 8 is a plan view of a large-sized apparatus, showing the supports for the sheets.

Fig. 9 is a cross section of the apparatus shown in Fig. 8.

Fig. 10 shows another construction.

. Fig. 11 shows'a device in which the conducting diaphragm is replaced by a double diaphragm, with the use of spacing pieces, and Fig. 12 shows a like device, without spacing pieces, and with the use of adhesion.

Fig. 13 shows another device in which the cemented points are replaced by elastic connecting points, means being provided for maintaining a partial vacuum in the pocket.

Fig. 14 is a detail view on a larger scale of a part of said pocket, the proportions being modified for the sake of clearness.

Fig. 15 showsanother device, and Fig. 16 another construction.

Fig. 17 shows the loud-speaking apparatus with a resonance box in which a vacuum or a pressure is produced.

Figs. 18 and 19 show respectively devices for producing a vacuum or a pressure in the middle pocket or recipient.

Fig. 1 shows in section a. frame a upon. which is stretched a wire gauze member I) which is permeable to air and whose weight or mass per unit surface is sufficiently large with reference to the mass represented by one-half wave length of sound in the air;'0 and 0 are metallic (or metallized) condenser sheets, and the silk fabric pieces d d serve to electrically insulate the said sheets from the wire gauze member I).

To allow the maximum space for the mechanical oscillation of the two -external sheets, the intermediate layer of insulation between the said sheets and the surface of the central member preferably consists of a substance which is uite compressible and elastic, such it?! silk fa ric,.thin Japanese paper, or the The central wire gauze. member may be made of silk-covered wire, and herein the metallic (or metallized) surfaces of the external condenser sheets may be placed in direct contact with this central member.

The external condenser plates may consist of thin sheets of rubber or gutta percha, celluloid or acetate of cellulose,or the like, which are metallized at the exterior by cementing thereto a thin leaf of metal, or by a like process, the said sheets being applied directly against the said central wire'gauze member and without interposing any other insulation. Herein the said metallized insulating sheet is applied upon the said central member according to the irregularities of its surface, and this will beusually suflicient to form supporting points between which the vibrations of the armatures may be produced.

A constant potential difference is maintained between the plates 0 and 0 by the batteries 6 and-e whose middle point f which may be grounded, is connected with the wire gauze member I) through the self-induction coil f coating with a like coil 9 adapted to receive the vibrational current which is to be converted into sound and which may be supplied from the last bulb h of an amplifier.

In Fig. 3, which shows a like arrangement for a loud-speaking outfit, the electric circuits are somewhat modified; one pole of the battery e is connected with the central member I), and the other pole is connected with the two plates 0 0 through the two self-induction coils f f which are wound in the same direction and are coupled to the self-induction coil 9 carrying the vibrational current.

In a modified apparatus, we may dispose a single condenser sheet against the said metallic member which is-permeable to air, so that the said sheet and member will form a condenser which is brought to a suitable difference of potential. For the operation as a loud speaker, the vibrational potential is superposed upon a constant potential. For-the operation as a microphone, the vibrations of the light condenser sheet will afford an oscillating potential.

Fig. 4 shows a modification which c6m-.

prises but a single sheet 3 the battery 6 malntalns a constant potential difference between the member I) and the sheet 0 and the casing i of the receiver, and the wires 7' connect the wire gauze member I) and the sheet 0 with a battery supplying the constant potential. The batteries 6 e 6 may be replaced by a suitable device for rectifying the alternating current such as are in common use in radio apparatus. The pressure of the air or gas between the sheets e e of the device shown in Fig. 1 may be regulated by' suitably acting upon the pipe 70, which communicates with thetightly closed space between the said sheets. I v

In a device which comprises but a single condenser sheet which is shown in Fig. 6, we may change the position of the single sheet 0 by suitably varying the pressure; herein we employ the diaphragm Z which is secured to the frame (1, thus forming an enclosed space m. The diaphragm Z might be placed on the other side of the sheet 0 as shown in Fig. 7.

The pressure between the said sheets may be produced by a great variety of means, and for instance by setting up a difference of level in a liquid contained in two communicatingvessels nn (Fig. 6). In this manner we may produce a pressure or a partial vacuum. -To produce a pressure, we may.

employ a bottle of compressed fluid 0, and may provide a discharge valve p upon the wall of the casing Z. We might utilize a I small air fan for this purpose, or like means.

For the construction of a loud speaking device of large size, the external sheets, for instance in the form of a stretched diaphragm, which consist of acetate of cellulose or celluloid and are metallized on the exterior, may be mechanically secured to the wire gauze member at a certain number of points either by cementing or by the use of a suitable frame, permeable to air, which is applied againstthe said sheets. The outer edges of the said diaphragms and of the wire gauze are made fluid tight, and a slight excess of pressure is produced between the sheets so as to counterbalance the electrostatic pressure and to slightly separate the diaphragms from the wire gauze member in order to give room for the oscillations.

The attaching points of the sheet .to the wire gauze member, which are uniformly distributed upon the surface of the loud speaking device, will prevent all separation of the diaphragm due to an excess of internal pressure, so that the electrostatic field between the said sheets will always be very strong. We suitably select the tension of the sheets consisting of diaphragms made of rubber, acetate of cellulose, celluloid and the like, as well as their thickness and the spacing of the said attaching points so as to give to the several vibrating regions of the sheets comprised between the said attaching points a proper period of vibration which has a very low value and is inaudible, or is above 3000 Vibrations so as to offer no prejudice to the reproduction of the voice.

As observed in Figs. 8 and 9, the said attaching points are uniformly distributed upon the whole surface of the loud-speaking device, and the sheets 0 0 are for instance cemented to the wire gauze b at the points p. e employ a slight excess of pressure which is supplied between the said sheets through the conduit 70, so as to separate the sheets to the proper degree between the points 1), as shown in Fig. 9, whereby the said armatures will have sufficient freedom to vibrate.

In a modified apparatus, we may place between the sheets and the wire gauze member suitable spacing pieces which are uniformly distributed, thus, producing a slight vacuum between the said sheets so as to properly reduce the distance between the wire gauze member and the sheets which are held apart by the said spacing pieces.

In the said modified apparatus, as shown in Fig. 10, the points of adhesion p are replaced by the spacing pieces q; we produce a partial vacuum between the said sheets through the conduit is, so as to bring the said sheets closer together between the spacing pieces 9. Instead of producing the partial vacuum or the excess of pressure between the sheets, such may be produced upon the external face of each sheet, by placing at a certain distance a light diaphragm so as to forma closed space. When the apparatus is used as a transmitter for a sound of a definite pitch, it may be provided with a resonance box. For the small sized apparatus, we

may dispense with the attaching points of the sheets and the wire gauzemember, these being secured together solely at the edge.

In Fig. 11, the conducting diaphragm consists of a double diaphragm consisting of two sheets of insulation 5 and 5 for instance of celluloid, acetate of cellulose, or the like which are cemented together around their periphery 13 so as to form a fiuidtight receptacle. Said sheets are metallized on their inner surfaces, by silvering or by like means, and the wire 14 which is brought out at the periphery 13 serves to connect the internal metallic layers with the battery 6. The other pole of said battery is connected to the wire gauze sheets 1 and 2 thus maintaining a constant potential difference between said metallic surfaces and said wire gauze sheets.

The undulatory electric current which is to be converted into sound is impressed on the primary winding 10 cooperating with a secondary winding 9 of a transformer adapted to alter the potential difference between said metallic surfaces and said wire gauze sheets. The double diaphragm 5 and 5* forms a sort of flat pocket which is connected by the tube 15 with a suitable device producing a slight vacuum or excess of pressure relatively to the atmospheric pressure. In Figs. 11 and 12, the device for varying the pressure is shown in the form of an apparatus 16 operating by the difference of level of a liquid.

The sheets 5 5 are maintained in the case of Fig. 11 at a very short distance from the wire gauze members 1 and 2, by the spacing members 17 which are distributed upon the surface. By slightly varying the pressure of the gas between the sheets 5 and 5 their shape may be somewhat changed and they may be thus caused to approach or to recede from the members 1 and 2 so as to obtain the proper distance while allowing the necessary freedom to oscillate. A certain compression will bring the sheets 5 and 5 closer to the members 1 and 2, thereby increasing the electrostatic field while allowing space for the vibration.

In Fig. 12, the sheets 5 5 are indirect contact with the wire gauze members 1-2. If the said sheets and members have a sulficient size, they may be connected together according to a series of points or lines, by a suitable cementing material at 18, the spacing of the parts between the cementing points being adjusted by varying the pressure in the interior of the middle pocket.

The electric arrangement is such that the members 5 5 will be moved at the same time to the right or left under the effect of the variations of potential.

In Fig. 13, the walls 5 5 of the middle pocket are applied against the wire gauze members 12 at various points by a plurality of elastic spacing members 17 which may consist of small knots formed on a rubber sheet or textile fabric such as wool, or the like. The textile fabric may have open meshes, or it may consist of a net with crossed or knotted threads.

The distance between the points of contact or adhesion may vary according to the thickness, the weight or the tension of the sheets. For instance, if the thickness of the membrane is a few hundredths of a millimeter, the distance between the contact points may be a few millimeters, whereas for a thickness of'0,1 to 0,2 mm. it may be a few centimeters.

In Fig. 13, 18 is a clamp which holds the rings 3 and 4 upon which the said wire gauze members are mounted. To produce a certain vacuum in the pocket, we employ the vessel 19 which contains water or other liquid at a pressure produced by the pump 20. The water discharged through the conduit 21 is heated by the electric resistance 22 and produces a slight stream of vapor at the orifice 23, so that air will be withdrawn from the pocket through the conduit 24, thus forming a partial vacuum in the said ocket. By supplying steam through the p1pe 15, an excess of pressure can be produced in the pocket. We may substitute carbonic acid gas under pressure for the steam.

Fig. 14 is a detail view on a larger scale showing the various parts of the device. The wire gauze members 12 are mounted on the frames 3-4. The pocket consists of acetate of cellulose and comprises two walls 5 and 5 which are silvered in the interior at and are connected with the electric circuit. At 18 'are shown the points at which-the sheet is cemented to the wire gauze members.

In the modification which is shown in Fig.

15, the rings 3 and 4 are provided, opposite the wire gauze members, with flexible diaphragms 26 '26 which form with the respective vibrating diaphragms 5 and 5 two fluidtight recipients in which an excess of pressure may be produced through the orifices 15. This excess of pressure will offer the same result as in the device shown in Fig. 13, i. e. it will slightly separate the wire gauze members from the diaphragms 5 ---5 between the cementing points.

A certain number of wire gauze members, with their respective diaphragms, may be placed in parallel position and at a slight distance apart, so as to increase the power of the loud speaking device. We may further dispose a plurality of elements in a given plane, in order to increase the wave-emitting surface and to obtain a directed set of acoustic waves.

We may employ the same apparatus, making the diaphragms 5 5 very thin, for producing sounds of a very high pitch, and even directed ultra-audible waves. The loudspeaking device may-further be used for the production of sounds or signals of a given pitch or amplitude, and herein the device comprises a resonance box or plate .whose bottom is parallel with the vibrating diaphragm. p

Should it be desired to produce a sound having a given frequency, or to use the apparatus as a loud speaker or as a-microphone, we may employ only a single diaphragm 5 which is placed against a single wire gauze member 1 (Fig. 16), with the optional use of a diaphragm 26 to produce an excess of pressure or a vacuum.

An apparatus for producing a sound having a stated frequency is shown in Fig. 17, in which 27 is the bottom of the resonance box whose distance from the diaphragm varies according to known laws, with the pitch of the sound to be produced; said box 27 may be made fluidtight and it will thus serve to produce a pressure or a vacuum in order to regulate the distance between the diaphragm 5 and the wire gauze member 1. This device shown in Fig. 17 may be supplied electrically by the use of a variable potential of the proper frequency between the wire gauze member 1 and the metallic layer of the diaphragm 5; the sound of the required pitch can be produced by employing alternating current of the corresponding frequency. A constant potential may be superposed, as shown in Fig. 17. If a resonance box is used, the diaphragm 5 may be much thicker, provided the wire gauze member 1 has a great inertia relatively-to that of the diaphragm.

Fig. 18 shows a device for maintaining a vacuum in the pocket or recipient. In the base of the apparatus is mounted a bellows 30 comprising a fixed bottom 32 and amovable top 31. The interior of the said bellows is connected with the interior of the pocket by the pipe 15. On the movable top is pivotally mounted the lever 33 whose end 34 extends to the exterior of the base and is adapted to receive a small weightv 35 which may be placed at various distances from the fulcrum of the lever 34. A position of equilibrium will be attained in which the action of the weight 35 is balanced by the action of the vacuum in the bellows'30. If the pocket is not completely tight, the leakage of air into the pocket which may take place very slowly will cause the lever 34 to descend, thus increasing the volume of the bellows 30 and automatically producing the vacuum corre-' sponding to a state of equilibrium.

As shown inFig. 19, the same device will serve to maintain a constant pressure in the said pocket. The fixed part of the bellows is shown at the bottom at 31, and the movable part 32 is now at the top. The lever' 34 and the weight 35 press upon the movable part 32 in order to compress the bellows 30 as far as the position of equilibrium corresponding to the proper pressure.

While we have described our invention in what we deem to be its preferable form, we do not wish to be limited thereto as vvarious changes might be made in the construction and arrangement of the constituent parts without departing from the spirit of the invention as comprehended within the scope of the appended claims.

What we claim is:

1. A device for the production of sounds by means of a modulated electric current, and inversely, which comprises two rigid sheets permeable to air, two vibrating diaphragms placed between said sheets, means for adjusting the distance between the said vibrating diaphragms and the said rigid sheets, means for applying a constant potential between said sheets and vibratingdiaphragms, and

means whereby the variable modulated potential to be transformed into sounds may be applied to the said vibrating diaphra s.

2. A device for the production 0 sounds by means of a modulated electric current, and inversely, which comprises two rigid sheets permeable to air, two vibrating diaphragms placed between said sheets, points 0 contact between the said vibrating diaphragms and the rigid sheets which points are suitably spaced upon the said vibrating diaphragms, means for regulating the distance between the vibrating diaphragms and the rigid sheets in the space between the several points of contact, means for applying a constant potential between the said rigid sheets and the vibrating surfaces, and means whereby the variable modulated potential to be transformed into sounds may be applied to the said vibrating diaphragms.

3. A device for the production of sounds by means of a modulated electric current, and inversely, which comprises two rigid sheets permeable to air, two vibrating diaphragnrs placed between said sheets, points of contact between the said vibrating diaphragms and the rigid sheets which points are suitably spaced upon the said vibrating diaphragms, means for producing a variation of pressure between the two vibrating diaphragms and for regulating the distance between the said vibrating dia hragms and the said rigid sheets, means or applying a constant potential between the said rigid sheets and the vibrating diaphragms, and means whereby the variable modulated potential to be transformed into sounds may be applied to said vibrating diaphragms.

4:. A device for the production of sounds by means of a modulated electric current, and inversely, which comprises two rigid sheets permeable to air, two internally metallized insulating sheets joined at their edges and adapted to form a fiat pocket disposed between the said rigid sheets, means whereby the said insulating sheets may be applied against the said rigid sheets at certain points, means for producin a pressure variation in the interior of said at pocket formed by the said insulating sheets, a constant potential applied between the said rigid sheets and said metallized sheets, and means whereby the variable modulated potential to be transformed into sounds may be applied to the said metallized sheets.

5. A device for the production of sounds by means of a modulated electric current, and inversely, which comprises a flat pocket, at least one wall of which is a vibrating diaphragm, rigid sheets permeable to air, means for applying a constant potential between said sheets on the one hand and vibrating diaphragm's on the other hand, means for adjusting the distance between the said vibrating diaphragms and the said sheets and means In testimony whereof we have signed this I specification.

CONSTANTIN OHILOWSKY. BORIS NAGACHEFF. 

